On the surface, Richard (Humphrey Bogart) and Kathryn Mason (Rose Hobart) appear to be a happily married couple. But on their fifth wedding anniversary, Kathryn accuses Richard of having fallen in love with her younger sister, Evelyn Turner (Alexis Smith), who is living with them. He does not deny it, but has resigned himself to leaving things as they are, since he is certain Kathryn would not give him a divorce. At a party celebrating the couple’s anniversary hosted by family friend and psychologist Dr. Mark Hamilton (Sydney Greenstreet), Richard becomes annoyed when Evelyn spends time with Mark’s handsome young colleague, Professor Norman Holdsworth (Charles Drake). On the way home, Kathryn suggests to Evelyn that their mother is lonely, so Evelyn decides to move home. Distracted by this unwelcome news, Richard crashes their car and suffers a broken leg. He then decides to take desperate action.

Richard pretends to require a wheelchair, even after his leg has healed; his puzzled physician, Doctor Grant (Grant Mitchell), diagnoses the problem as psychological, not physical. He suggests exercise, so a car trip to a mountain resort is arranged. At the last minute, Richard has to stay home to do some work; he has Kathryn go on ahead by herself. She is blocked on a narrow deserted mountain road by a parked car. Richard walks unexpectedly out of the fog and kills her. Afterward, he pushes her car down a steep slope; it dislodges some logs which crash down and hide the automobile. He returns home in time to set up an alibi by meeting with employees he had summoned. He then notifies the police that she is missing.

…

The film is rather unique in that it is the only one which Bogart and Greenstreet co-starred and Greenstreet was not a villain or a corrupt character, but rather Bogart was.